This invention relates to diagnostic assay modules for analytical applications and, more particularly, it concerns assay modules including a resilient assay element wherein the interaction of a component in a sample fluid with one or more reagents present in the assay element causes a detectable change corresponding to the presence of the sample component.
In commonly assigned, copending U.S. patent application Ser. No. 210,732, filed June 23, 1988, entitled "LIQUID TRANSPORT SYSTEM", there is disclosed a liquid transport device which is particularly suited for use in immunoassay applications. In such applications a surface of an assay element is retained in contact or virtual contact with a relieved surface on the underside of a member which includes an aperture for allowing a sample fluid to be applied and distributed uniformly over the surface of the assay element. The relieved surface is defined by a plurality of projections arranged throughout the fluid flow zone to control the flow of fluid between opposed surfaces of the fluid flow zone. In a preferred embodiment the projections are arranged in orthogonal rows and columns to provide a uniform distribution of a sample fluid across the surface of an assay element. The positioning of the assay element in contact or virtual contact with the projections controls the volume of fluid in the fluid flow zone.
In addition to ensuring a uniform spread of the fluid sample across the surface of the assay element, the disclosure in this copending application recognizes the importance of retaining the assay element in a desired orientation to provide, among other purposes, for optical precision where the change resulting from interaction of a sample analyte with the assay element reagent(s) is read out by means of an optical apparatus. Retention of the assay element in such an orientation can be achieved by a support member arranged to engage the surface of the assay element in a manner to sandwich the element between a surface on the support member and the relieved surface. The support member is provided with a transparent window through which the change in the assay element may be read by the optical system. This arrangement is not completely satisfactory in all instances since the electromagnetic radiation used to read the change in the assay element must pass through the material from which the support member is made. Where relatively small changes are being read it may be more desirable not to interpose anything between the assay element and the optical system.
In another commonly assigned, copending U.S. patent application Ser. No. 378,647 filed July 12, 1989, entitled, "OPTICAL READ SYSTEM AND IMMUNOASSAY METHOD" now U.S. Pat. No. 4,977,325, a highly efficient dual channel fluorometer is disclosed in which enhanced optical efficiency enables the use of a low cost tungsten halogen illumination source in combination with solid state photodetectors to detect the low levels of sample emitted light encountered in fluoroanalysis. The optical system is embodied in an optics head designed to be positioned under a sample receiving vessel of the general type represented by the physical embodiment disclosed in the aforementioned copending application Ser. No. 210,732.
It is apparent from the combined disclosures of the aforementioned patent applications that the attainment of reliable results in analytical procedures requires the assay module in which the assay element is contained to accommodate the requirements for obtaining a uniform spread of the sample fluid across the surface of the assay element, for volume control of the fluid in a fluid flow zone where applicable and retention of the assay element under conditions which optimize the optical system by which the optical signal is read from the assay element. In this context, inclusion of a transparent window in the path of light directed to and reflected from the surface of the assay element represents an efficiency loss in the optical system of a magnitude which may have a substantial effect on the accuracy of the overall diagnostic equipment.